I can relate to your op, lisa72. For me it seemed like the anger just sort of showed up one day when my dd1 was about 2 1/2 and was like a mooching relative that came to visit but never left. The good news is that now the anger feels normal and is not a constant companion. Things have been steadily improving for a long while now.
Here's what worked for me in a nutshell:
First, I had to both recognize that I was angry and accept it. Then I had to accept that anger is indeed a normal, human emotion so though I can reduce the amount of anger I feel I can't permanently eliminate it-I have to be able to feel angry without feeling like a bad person because of it, kwim?
Once I examined those two things, I realized (as you probably do) that it's not the feeling of anger itself that is the problem. The problem is my reactions: the things I do and say out of anger, the thoughts I indulge in out of anger that produce more anger. I also realized that focusing on "Try Not to Yell" or Try Not to Get Angry" was a little like someone coming in and telling me "Try not to think of an elephant!"-well, of course I'm going to think of an elephant, and pretty quickly. Likewise when my goal is "Don't lose my cool" or "Don't yell" I'm actually pretty likely to yell because yelling or otherwise losing my cool is what I'm thinking about.
What has helped the most is to simply pay attention to my reactions: when they happen, why, what's going on, how do I feel physically, what am I thinking, what am I feeling besides anger, what do I want, what do I expect, etc. To pay attention meant that paying attention, not stopping a bad habit, was my goal for a time (just as often we know that the key to resolving a child's behavior problem is understanding why it's happening, so we take some time to listen and understand first rather than just trying to stop the behavior) . This was really hard, because I learned some things about myself that weren't very comfortable or flattering. But it was extremely helpful. It allowed me to really recognize what I was doing and why-and more often than not I saw that the anger came as a secondary emotion, that there was something else beneath that anger. Sometimes I couldn't see what was going on until after I'd already reacted and it was over, sometimes I saw what was going on as I was in the thick of losing my cool, sometimes I saw it in the split second before I yelled at my kids.
Soon enough seeing what was going on led to being able to pause-maybe just before I would have reacted badly, maybe as I was reacting, maybe not until after. And pausing was so important, regardless of when it happened, because in that pause was the ability to see and make the choice: yell (or react in some hurtful way), or say/do something else, or do nothing. Often I chose to do nothing rather than yell/otherwise lose my cool, because I didn't yet know what to do that would be right and doing nothing was better than doing something that would be hurtful. But as time went on it was that pause that let me see all the things I could do or think or say, whether in that one moment or in general (like get more sleep). And often just being aware of my own thoughts and feeings was enough to allow me to let the anger go.
I second the recommendation of the book "When Anger Hurts Your Kids". I would also recommend something like "Wherever You Go There You Are", "Peace Is Every Step", "Waking Up to What You Do" or other books on cultivating mindfulness within yourself. In my growth as a parent, learning to be present in the moment and aware of not just what's going on with my kids, but also of what's going on within myself has been more important than just about anything else.